Motor cooling means for hermetically sealed refrigerant compressor unit



Jan. 8, 1957 K. K COOPER 2,776,542

MOTOR COOLING MEANS FOR HERMETICALLY SEALED REFRIGERANT COMPRESSOR UNIT Flled July 7, 1955 INVENTOR.

KENNETH K. COOPER HIS ATTORNEY United States Patent MOTOR COOLING MEANS FOR HERMETICALLY SEALED REFREGERANT COMPRESSOR UNIT Kenneth K. Cooper, North Caldwell, N. J., assignor to General Electric Company, a corporation of New York Application July 7, 1955, Serial No. 520,600

11 Claims. (Cl. 62-3) The present invention relates to hermetically sealed refrigerant compressor units and is more particularly concerned with an improved means for cooling such units.

A hermetic refrigerant compressor unit ordinarily comprises a sealed casing in which is disposed a refrigerant compressor and a motor for driving the compressor. As the compressor and motor are enclosed in the sealed casing and are mounted in spaced relationship with the walls defining the casing, some means must be provided for cooling the compressor and motor. Ordinarily the refrigerant charge in the refrigerant system of which the hermetic motor compressor unit forms a part is employed for this purpose. When low pressure refrigerant gas (suction gas) is used to cool the unit, the motor gives up its losses in the form of heat to that gas and is thereby cooled. The same is true of the compressor although to a lesser extent, since some of the heat given up by the compressor is carried off with the refrigerant discharged from the compressor. However, the heat absorbed by the suction gas prior to compression thereof in the compressor causes an increase in its entropy as well as an increase in its temperature and thus may effect a loss in eificiency which may be of the order of 20% of the useful work being done on the refrigerant. To avoid this loss of efficiency, various arrangements have been proposed for using the high pressure refrigerant discharged from the compressor to cool the motor as the compressor the-n does not have to compress the refrigerant after the motor heat has been added thereto. However, the discharge gas from the compressor is usually too hot to maintain the motor, particularly for the larger units, at safe operating temperatures. To obtain the advantages of discharge gas cooling of the motor and in an attempt to overcome the disadvantages thereof, it has also been proposed to mix condensed refrigerant from the refrigerating system with the compressor discharge gas and to pass this mixture over the motor for the cooling thereof. Such arrangements have not been completely satisfactory. A relatively large amount of condensed refrigerant must be mixed with the hot compressor discharge gas in order to lower the temperature of the mixture to that which will effectively cool the motor yet the amount of liquid refrigerant introduced into the casing must not be so great that unevaporated liquid refrigerant can collect in the oil sump or reservoir normally provided in the casing.

It is an object of the present invention to provide an improved arrangement for employing liquid refrigerant in cooling the motor of a hermetically sealed motor compressor unit.

Another object of the invention is to provide means for employing condensed refrigerant to cool the motor of a hermetically sealed unit and to control the amount of condensed refrigerant introduced into said sealed unit to that which will be completely vaporized during circulation thereof over the motor and prior to the passage thereof from the motor compressor unit into the casing.

A further object of the invention is to provide positive means for passing condensed refrigerant in heat exchange relationship with the motor of a hermetic compressor unit and means responsive to the load on the compressor for limiting the amount of condensed refrigerant to that which is snfiicient to cool the motor but is insufficient to cause the accumulation of liquid refrigerant within said casing.

Further objects and advantages of the invention will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

In accordance with the present invention there is provided a hermetically sealed refrigerant compressor unit adapted to form part of a refrigerating system including condenser means for condensing the refrigerant compressed by the unit and evaporator means for evaporating the condensed refrigerant. The hermetically sealed unit includes, in addition to compressor means, a motor for driving the compressor means and means for passing controlled amounts of liquid or condensed refrigerant from the refrigerating system in heat exchange relationship with the motor. In order to control the amount of liquid refrigerant passing over the motor, there is provided a thermally operated valve sensitive to the ambient conditions within the hermetic casing and adapted to limit the amount of liquid refrigerant to that which will be completely evaporated by the heat of the motor and by admixture with the compressed refrigerant discharged from the compressor. In the preferred form of the invention, the thermally responsive means employed to control the operation of the valve comprises a refrigerant-filled bellows disposed within the casing and hence surrounded by the compressed refrigerant discharged from the compressor whereby the amount of liquid refrigerant passed in cooling relation with the motor can be controlled in a manner that maintains essentially a constant superheat of the high pressure gaseous refrigerant within the casing to assure complete evaporation of the liquid refrigerant used to cool the motor.

For a better understanding of this invention, reference may be had to the accompanying drawing in which the single figure is a somewhat schematic, side elevational view, partially in section, of a refrigeration system incorporating an embodiment of this invention.

Referring to the drawing there is shown a hermetically sealed refrigerant compressor unit 1 forming part of a closed refrigerating system including a condenser 2, a suitable expansion device such as the capillary tube 3, and an evaporator 4. These elements comprise the usual closed refrigerating system in which a refrigerant charge is compressed in the sealed unit 1, condensed in the condenser 2, and evaporated in the low pressure side of the system including the evaporator 4 from which the refrigerant vapor is Withdrawn by the unit 1.

The sealed unit 1 essentially comprises a hermetic casing 5 and a motor compressor unit comprising a compressor 6, which is preferably a rotary compressor, and an electric motor 7 for driving the compressor. The motor compressor unit is supported within the casing 5 in spaced relationship with the walls forming the casing 5 by suitable supporting means (not shown). During operation of the compressor, low pressure refrigerant is withdrawn from the evaporator 4 through the suction line 8 and the compressed refrigerant discharged by the compressor through suitable discharge ports 9 into an annular chamber 11 between the compressor 6 and the frame member 12 surrounding and supporting the compressor 6. Fromthe annular chamber 11, the hot compressed refrigerant passes through apertures 13 provided in the frame 12 into the interior of the sealed casing 5. From the casing 5 the refrigerant flows through the outlet conduit 14- to the condenser 2. In this type of unit, it will be seen that the sealed casing 5 is entirely filled with high pressure refrigerant, that is, refrigerant at compressor discharge pressures.

A particular advantage of a hermetic compressor unit of this type in which the compressor discharges into the casing concerns the ease with which entrained lubricating oil can be separated from the compressed refrigerant. The lubricating oil is supplied by suitable lubricating means (not shown) from the oil sump to the various moving parts of the motor 7 and compressor 6. Particles or droplet of the lubricant suspended in the compressor discharge gas settle out by gravity from the discharge gas stream during the period of time that the discharge gas remains within the casing 5 and return to the oil sump 15. This eliminates the need for any special oil separating means between the unit 1 and the condenser 2 such as are required if the casing 55 is filled with suction gas and the compressed gas or refrigerant from the comprcssor 6 is introduced directly into the high pressure line connecting the unit 1 to the condenser 2.

However this advantage is offset by the difiiculties involved in cooling the unit, particularly the motor 7. Since the discharge gas within the casing 5 is at a relatively high temperature which, particularly in the case of larger units, is too high to effectively remove the heat losses of the motor 7, it is necessary to provide some other means for maintaining the motor 7 at efiicient and safe operating temperatures. Accordingly there is provided by the present invention means for directing a coolant in the form of condensed refrigerant from the refrigerating system over the motor 7 whereby the evaporation of this liquid refrigerant effectively cools the motor with no significant increase in the load on the compressor 6.

In order to maintain the coolant in intimate heat exchange relationship with the motor there is provided a housing 13 substantially surrounding the motor 7 in slightly spaced relationship therewith. A pump 19 arranged at the upper end of the housing 13 and driven by the motor 7 Withdraws liquid or condensed refrigerant through a conduit 20 from the refrigerating system between the condenser 2 and the expansion device or capillary tube 3 and this liquid refrigerant which is discharged by the pump 19 into the interior of the housing 13 flows in a path generally indicated by the solid arrows downwardly over and through the motor 7 in intimate heat exchange relationship with the various parts thereof. Most of the liquid refrigerant is evaporated by the heat of the motor 7 and the resultant refrigerant vapor, whose flow path is generally indicated by the dotted arrows, passes out of the housing 18 through suitable openings '22 provided at the bottom of the housing. The openings 22 are adjacent to and communicate directly with the discharge port 9 of the compressor 6 so that any liquid refrigerant leaving the housing 18 is immediately mixed with the hot discharge ga and is evaporated thereby be fore passing through the apertures 13 into the main portion of the casing 5.

To regulate the amount of liquid refrigerant pumped by the pump 19 into the housing 18 to an amount suflicient to cool the motor 7 but less than that which would result in liquid refrigerant passing through the apertures 13 into the casing 5 with the possibility that it may collect in the oil sump 15, there is provided in the conduit 20 a thermally operated valve 24 which controls the flow of liquid refrigerant to the pump 19 in accordance with the cooling requirements. It is desirable that the valve 24 supply the maximum amount of liquid refrigerant to the pump 19 and hence to the housing 18 when the cooling requirements are high and to decrease the amount of liquid refrigerant when the cooling requirements are low. To obtain these results in accordance with the preferred embodiment of the invention, the valve 24 is operated by a thermally responsive device such as the bellows 25 positioned within the casing 5 and surrounded by the hot compressed refrigerant within the casing. Opening of the valve 24 introduces compressed refrigerant gas from within the casing 5 through the valve port 26 and into the conduit 20 thereby decreasing the amount of liquid refrigerant drawn through the conduit 20 by the pump 19. On the other hand, the expansion of the bellows 25 closes the valve port 26 so that the entire pumping capacity of the pump 19 is used to supply liquid refrigerant from the condenser 2 to the motor 7 for maximum cooling. Additional means for controlling or regulating the operation of the valve 24 may be provided in the form of a spring 28.

The valve 24 and particularly the thermal control element 25 are positioned within the casing 5 between the compressor and the conduit 14. With the thermal elemeat 25 so positioned, the high pressure gas surrounding thi element is composed of a mixture of the compressed refrigerant discharged by the compressor 6 and the evaporated refrigerant from the motor housing 18. Therefore by regulating the operation of the valve 24 to maintain the temperature of this gas mixture surrounding the element 25 at a temperature somewhat above the boiling point or evaporating temperature of the refrigerant under the pressure conditions existing within the casing 5, complete evaporation of any excess liquid refrigerant flowing from the housing 18 through the aperture 22 i assured upon the mixing of this liquid refrigerant with the hot gas discharged from the compressor 6 into the chamber 11.

While any suitable temperature responsive element can be employed to open and close valve 24 in response to changes in temperature of the high pressure refrigerant within the casing 5, which temperature changes are a measure of the motor cooling requirements, the element 25 for controlling the valve 24 is preferably a metallic bellows charged with the same refrigerant with which the system is charged. Its internal pressure is then proportional to the temperature and as the external pressure on the bellows is of course the compressor discharge pressure, the operation of the valve is sensitive to the difference between the discharge temperature and pressure or in other words to the superheat of the hot gas contacting the bellows 25 regardless of operating conditions.

During operation of the cooling system in its preferred form, the pump 19 of course operates whenever the unit 1 is running. Compressed refrigerant from the compressor 6 is discharged into the casing 5 and from there flows through the discharge conduit 14 to the condenser 2 where it is condensed or liquefied. During the initial operation of the system the temperatures within the easing 5 may be relatively low and the motor 7 relatively cool. Under these conditions the motor requires subszantially no cooling and the valve 24 may be so regulated that it is fully open and substantially no liquid refrigerant is withdrawn from the refrigerating system by the pump 19. Further operation of the system resulting in a gradual increase in the temperature of the discharge gas surrounding the bellows 25 will cause the bellows 25 to expand and thereby decrease the relative amount of compressed gas introduced into the conduit 20 through the valve port 26. As a result, the amount of liquid refrigerant introduced by the pump 19 into the housing 18 gradually increases in proportion to the increased load and therefore the increased cooling requirements of the motor 7. By setting the valve 24 to maintain a given degree of superheat in the high pressure gaseous refrigerant surrounding the bellows 25, the amount of liquid refrigerant supplied by the pump 19 to the motor 7 will always be suflicient to cool the motor 7 but will not be so much but that .the discharge gas issuing from the discharge port 9 will completely vaporize any liquid refrigerant flowing through the opening 22 from within the housing 18. In other words since the compressed refrigerant discharged by the compressor 6 into the chamber ll will always have a higher degree of superheat than any mixture of this gas with the evaporated refrigerant from the housing 13 contacting the bellows 25, a setting of the valve 24.- to maintain a given constant superheat of the discharge gas mixture surrounding the bellows 25 will assure complete evaporation of the liquid refrigerant within the chamber 11 and will prevent any liquid refrigerant from collecting or settling into the oil sump 15.

From an oil separation point of view, the advantages of the present system are believed obvious. The oil is separated from the gas discharged from the compressor as this gas is mixed with the liquid refrigerant or relatively cool refrigerant vapor from within the housing 18 which may also contain some oil from the motor bearings within the housing 18. These oil particles separate by gravity from the high pressure refrigerant either after it has passed through the apertures 13 to the main portion of the casing 5 or within the chamber 11 from which the oil will return to the oil sump 15 through suitable drains 3i provided in the bottom portion of the frame it.

While there has been shown and described a specific embodiment of the present invention, it is to be understood that the invention is not limited to the particular form shown and described and it is intended by the appended claims to cover all modifications within the spirit and scope of the invention' What I claim as new and desire to secure by Letters Patent of the United States is:

1. A hermetically sealed refrigerant compressor unit comprising a sealed casing, compressor means disposed within said casing including means for withdrawing low pressure refrigerant from a refrigerating system and for discharging compressed refrigerant into said casing, a motor for driving said compressor means, and means including a thermally operated valve for passing condensed refrigerant in heat exchange relationship with said motor, said valve controlling the amount of condensed refrigerant passed through said motor in accordance with the temperature of the compressed refrigerant in said casing.

2. A hermetically sealed refrigerant compressor unit comprising a sealed casing, rotary compressor means disposed within said casing including means for withdrawing low pressure refrigerant from a refrigerating system and for discharging compressed refrigerant into said casing, a motor for driving said compressor means, and means including a bellows operated valve for passing liquid refrigerant in heat exchange relationship with said motor, said valve and bellows being disposed within said casing and controlling the flow of liquid refrigerant through said motor in accordance with the pressure and temperature conditions of the compressed refrigerant surrounding said bellows.

3. A hermetically sealed refrigerant compressor unit comprising a sealed casing, compressor means disposed within said casing and adapted to discharge compressed refrigerant into said casing, a motor for driving said compressor means, means for controlling the motor temperature in accordance with the load placed on said compressor, said temperature controlling means comprising conduit means for passing condensed refrigerant in heat exchange relationship with said motor, valve means for controlling the flow of condensed refrigerant through said conduit means, and thermal means for controlling said valve responsive to the temperature of compressed refrigerant Within said casing.

4. A hermetically sealed refrigerant compressor unit comprising a sealed casing, rotary compressor means disposed within said casing and adapted to discharge compressed refrigerant into said casing, a motor for driving said compressor means, means for directing c011- densed refrigerant in cooling contact with said motor in amounts proportional to the load placed on said compressor, said directing means including a valve for controlling the fiow of condensed refrigerant to said motor and thermal means for controlling said valve responsive to the temperature of compressed refrigerant within said casing.

55. A hermetically sealed refrigerant compressor unit comprising a sealed casing, a compressor within said casing including means for withdrawing low pressure refrigerant from a refrigerating system and for discharging compressed refrigerant into said casing, a motor for driving said compressor, a housing within said casing enclosing said motor and having an opening therein adjacent one end of said motor communicating with the interior of said casing, and means for cooling said motor comprising a conduit for introducing liquid condensed refrigerant into the other end of said housing and means for introducing compressed refrigerant from Within said casing into said conduit in amounts inversely proportional to the temperature of the compressed refrigerant Within said casing.

6. A hermetically sealed refrigerant compressor unit comprising a sealed casing, a rotary compressor within said casing including means for withdrawing low pressure refrigerant from a refrigerating system and for discharging compressed refrigerant into said casing, a motor for driving said compressor, means for cooling said motor comprising a housing within said casing enclosing said motor and having an inlet at one end and an outlet at the other end with the interior of said casing adjacent said compressor, a conduit means including a pump driven by said motor for introducing liquid condensed refrigerant into the inlet in said housing and means for pumping compressed refrigerant from within said casing into said conduit ahead of said pump in amounts inversely proportional to the temperature of the compressed refrigerant within said casing to control the amount of liquid refrigerant pumped into said housing.

7. A hermetically sealed refrigerant compressor unit comprising a sealed casing, compressor means for withdrawing low pressure refrigerant from a refrigerating system and discharging compressed refrigerant into said casing, a motor for driving said compressor means, means for directing condensed refrigerant from said system into heat exchange relationship with said motor in an amount proportional to the load on said motor, said directing means including a valve for admitting compressed refrigerant from within said easing into said directing means, a bellows for controlling the operation of said valve, said bellows being charged with refrigerant and being disposed within said casing in direct heat exchange relationship with the compressed refrigerant discharged from said compressor whereby the pressure within said bellows is proportional to the temperature of the compressed refrigerant within said casing and the external pressure on said bellows is equal to the pressure of said compressed refrigerant within said casing with the result that the said valve controlled by said bellows is sensitive to the degree of superheat of said compressed refrigerant.

8. A hermetically sealed refrigerant compressor unit comprising a sealed casing, a compressor means for withdrawing low pressure refrigerant from a refrigerating system and discharging compressed refrigerant into said casing, a motor for driving said compressor means, means for directing condensed refrigerant into heat exchange re lationship with said motor in an amount proportional to the load on said motor, said directing means including a housing surrounding said motor and a conduit con necting said housing to a source of liquid refrigerant in said system, a valve in said conduit for admitting compressed refrigerant from within said casing into said conduit to control the amount of liquid refrigerant flowing through said conduit, a bellows for controlling the operation of said valve, said bellows being charged with refrigerant and being disposed within said casing in direct heat exchange relationship with the compressed refrigerant discharged from said compressor whereby the pressure within said bellows is proportional to the temperature of the compressed refrigerant within said casing and the external pressure of said bellows is equal to the pressure of said compressed refrigerant within said casing with the result that the amount of compressed refrigerant admitted to said conduit is inversely proportional to the degree of superheat of the compressed refrigerant in contact with said bellows.

9. A hermetically sealed refrigerant compressor unit comprising a sealed casing, a rotary refrigerant compressor including means for withdrawing low pressure refrigerant from a refrigerating system and a discharge port through which compressed refrigerant is discharged into the lower portion of said casing, a motor for driving said compressor disposed within said casing above said compressor, a housing surrounding said motor, an outlet in said casing for conducting compressed refrigerant to a refrigerating system, means for cooling said motor in eluding a pump and conduit connected to said pump for withdrawing condensed refrigerant from said refrigerating system and introducing said condensed refrigerant into said housing, an opening in the lower end of said housing communicating with said discharge port for passage of refrigerant from said housing into said casing, means for controliin the flow of condensed refrigerant introduced into said housing to an amount which is sufficient to cool said motor but which will completely vaporize within said casing, said control means including a valve for admitting controlled amounts of compressed refrigerant from with said casing into said conduit and a bellows char ed with refrigerant for controlling the operation of said valve, said bellows being positioned within said casing between said discharge port and said outlet from said casing and in heat exchange relationship with the compressed refrigerant contained therein, said refrigerant-filled bellows being adapted to maintain a predetermined degree of superheat in the compressed refrigerant surrounding said bellows to assure complete evaporation of the condensed refrigerant introduced into said housing.

E0. A hermetically sealed refrigerant compressor. unit comprising a sealed casing, a refrigerant compressor including means for withdrawing low pressure refrigerant from a refrigerating system and a discharge port through which compressed refrigerant is discharged into the lower portion of said casing, a motor for driving said cornprcsso-r disposed with said casing above said compressor, a housing surrounding said motor and having an opening at the lower end thereof communicating with said com- -or discharge port, an outlet in said casing for conting compressed ref' 131i from said casing to said refrigerating system, means for cooling said motor including a pump and a cond t connected to said pump for withdrawing condensed re rigerant from said refrigerating system and introducing said condensed refrigerant into the upper portion of said housing, means or controlling the fiow of condensed refrigerant introduced to said housmg to an amount such that all of the liquid condensed refrigerant is vaporized within said casing, said control means comprising a valve for admitting compressed refrigerant from within said easing into said conduit ahead of said pump and a bellows for controlling the operation of said valve, said bellows being charged with refrigerant and being positioned within said casing between said discharge port and said outlet from said casing, and in direct heat exchange relationship with the compressed refrigerant in said casing whereby said bellows is externally subjected to the pressure of the compressed refrigerant within said casing and its internal pressure is proportional to the temperature of said compressed refrigerant within said casing so that the operation of said valve by said bellows is controlled by the supcrheat of the compressed refrigerant surrounding said bellows, and means for regulating the operation of said valve to maintain a predetermined degree of superheat in the mixture of the refrigerant flowing through said housing and the compressed refrigerant discharged by said compressor.

ll. A hermetically sealed refrigerant compressor unit comprising a sealed casing, a rotary refrigerant compressor including means for withdrawing low pressure refrigerant from a refrigerating system and a discharge port through which compressed refrigerant is discharged into the lower portion of said casing, a motor for driving said compressor disposed with said casing above said compressor, a housing surrounding said motor an outlet in said casing for conducting compressed refri ant from said casing to said refrigerating system, means for cooling said motor including a pump and conduit connected to said pump for withdrawing condensed refrigerant from said refrigerating system and introducing said condensed refrigerant into the upper portion of aid hous ing, an opening at the lower end of said housing communicating with said compressor discharge port for the passage of refrigerant from said housing to said discharge port, means for controlling the flow of condensed refrigerant introduced to said housing to an amount such that all of the liquid condensed refrigerant is vaporized within said casing before passing through said opening, said control means comprising a valve for admitting compressed refrigerant from said casing into said conduit ahead of said pump to control the how of liquid refrig erant to said housing and a bellows for controlling the operation of said valve, said bellows being charged with refrigerant and being positioned within said casing between said discharge port and said outlet from said casing in direct heat exchange relationship with the compressed refrigerant in said casing whereby said bellows is externally subjected to the pressure of the compressed refrigerant within said casing and its internal pressure is proportional to the temperature of said compressed refrigerant Within said casing so that the operation of said refrigerant-charged valve by said bellows is controlled by the superheat of the compressed refrigerant surrounding said bellows, and means for regulating the operation of said valve to maintain a predetermined degree of superheat in the compressed refrigerant surrounding said bellows and assure complete evaporation within said housmg and discharge port of the liquid refrigerant introduced into said housing.

References Cited in the file of this patent UNITED STATES PATENTS 1,890,205 Andresen Dec. 6, 1932 2,040,507 Terry May 12, 1936 2,247,950 Kucher s July 1, 1941 

